Radial foil bearing

ABSTRACT

The radial foil bearing includes: a top foil; an intermediate foil; a back foil; and a bearing housing accommodating the top foil, the intermediate foil and the back foil. The top foil is formed by winding a rectangular metal foil which includes a first uneven portion and a second uneven portion, into a cylindrical shape so as to overlap the first and second uneven portions with each other, wherein the first uneven portion is composed of a projecting portion and a depressed portion formed on one edge of the metal foil, and the second uneven portion is composed of a depressed portion, and a projecting portion formed on another edge of the metal foil. The projecting portions of the first and second uneven portions pulled out near the bearing housing engage with engagement grooves of the hearing housing.

This application is a Continuation Application based on InternationalApplication No. PCT/JP2013/071791, filed Aug. 12, 2013, which claimspriority on Japanese Patent Application No. 2012-179776, filed Aug. 14,2012, the contents of both of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a radial foil bearing.

BACKGROUND ART

In the related art, as a bearing used for a high-speed rotating body, aradial bearing is known which is used in a state of being attached to arotary shaft so as to encircle the shaft. As such a radial bearing, aradial foil bearing is well known, including a thin sheet-shaped to foilwhich forms the bearing surface, a back foil which elastically supportsthe top foil, and a cylindrical bearing housing which accommodates thetop foil and the back foil. As the back foil of the radial foil bearing,a bump foil is mainly used in which a thin sheet is formed in a wavesheet shape.

In some foil bearings, for example, in order to improve the dampingeffect using friction between foils or to increase the rigidity of thetop foil, an intermediate foil is inserted between the top foil and theback foil (refer to Patent Document 1).

In such a radial foil bearing, in general, in order to prevent thedetachment of the top foil or the bump foil from the bearing housing,one end portion (toe portion) thereof is directly fixed to the bearinghousing or is indirectly fixed thereto via a spacer, using spot welding.Additionally, in general, the intermediate foil is disposed on theentire circumference of the bearing housing similarly to the top foil,and one end portion thereof is also fixed to the bearing housing throughwelding.

In addition, in Patent Document 2, without using welding, both ends(both ends in the circumferential direction) of a top foil are locked bybeing thrust against fixing walls of the inner wall of a housing, to befixed thereto.

DOCUMENT OF RELATED ART Patent Document

[Patent Document 1] U.S. Pat. No. 5,902,049

[Patent Document 2] Japanese Unexamined Patent Application, FirstPublication No. 2006-57828

SUMMARY OF INVENTION Technical Problem

However, the welding on the top foil has a high possibility thatdistortion occurs in the top foil because heat of the welding is appliedthereto. Similarly, the welding on the intermediate foil also has a highpossibility that the top foil is distorted. That is, if distortionoccurs in the intermediate foil due to welding, the distortion of theintermediate foil is reflected in the top foil which is disposed on theintermediate foil, and thus distortion may occur in the top foil. Inaddition, even if the top foil and the intermediate foil overlappingwith each other are welded at the same time, the distortion of theintermediate foil composing a lower layer is reflected in the top foil,and thus the amount of distortion of the top foil may be increased.

A structure is also known in which one end portion (toe portion) of atop foil is bent through bending machining in order to performmechanical fixing instead of welding. However, in this case, distortionmay occur in the top foil due to bending machining. Furthermore, inPatent Document 2, since both ends of the top foil are thrust againstthe fixing walls, reaction force is added to the top foil from both endportions toward the center portion thereof, and thus distortion mayoccur in the top foil.

The thickness of a fluid lubrication film of the foil bearing, which isformed between the rotary shaft and the top foil through rotation of therotary shaft, is very thin such as about 10 μm. Accordingly, even ifslight distortion occurs in the top foil, the load capability or thedynamic characteristics (the rigidity and the damping performance) ofthe bearing is influenced, and the designed performance thereof may notbe obtained.

In a normal top foil in which one end portion (toe portion) thereof isfixed to the bearing housing through spot welding, it is difficult tofit portions near both ends (a portion near the fixed end and a portionnear the free end) of the top foil into a curved surface composing theinner circumferential surface of the bearing housing, and the portionsnear both ends thereof may become close to be flat. Then, force (localpreload) clamping the rotary shaft occurs at the portions being close tobe flat, and as a result, problems may occur that the starting torque isincreased, the amount of heat generated during operation exceeds the setvalue, or the like.

In Patent Document 2, since distortion may occur in the top foil due tothe above-described reaction force, the top foil may not become close toa true circular shape along the inner circumferential surface of thebearing housing, and may become close to a polygonal shape partiallyincluding a flat portion due to the distortion. Then, a portion near theflat portion strongly contacts the rotary shaft, and thus force (localpreload) clamping the rotary shaft may occur. Therefore, the startingtorque may be increased, and the amount of heat generated duringoperation may exceed the set value.

In order to decrease such force (local preload) clamping the rotaryshaft, for example, it is conceivable that peaks of the bump foil (backfoil) are removed which support portions near both ends of the top foil.However, if the peaks of the bump foil are removed, the support rigidityfor the rotary shaft may significantly decreases at sections in whichthe peaks are removed. Accordingly, the movement of the rotary shafttoward the sections due to an impact load or the like cannot berestricted, and this structure has a high possibility that a rotatingportion such as an impeller provided in the rotary shaft contacts astationary portion (housing).

In addition, in order to prevent large decrease of the support rigidityfor the rotary shaft at the above sections, it is conceivable that theheight of only one peak of the bump foil is decreased at the abovesections. However, the amount of decrease of the height is small such asseveral tens of micrometers, and thus the manufacturing thereof is verydifficult.

The present invention was made in view of the above circumstances, and afirst object thereof is to provide a radial foil bearing in which thedesigned favorable performance of the bearing can be obtained withrespect to the load capability and the dynamic characteristics (therigidity and the damping performance) thereof by sufficiently decreasingdistortion which occurs in a top foil, the damping effect can beimproved using the friction between foils, and the machining costthereof can be reduced. In addition, a second object thereof is toprovide a radial foil bearing which can prevent the occurrence of force(local preload) clamping a rotary shaft.

Solution to Problem

According to a first aspect of the present invention, a radial foilbearing used for supporting a rotary shaft so as to encircle the rotaryshaft, the radial foil bearing includes: a cylindrical top foil disposedso as to face the rotary shaft; an intermediate foil disposed outside ofthe top foil in a radial direction thereof; a back foil disposed outsideof the intermediate foil in the radial direction; and a cylindricalbearing housing accommodating the top foil, the intermediate foil andthe back foil. Engagement grooves are formed on an inner circumferentialsurface of the bearing housing in an axial direction thereof The topfoil is formed by winding a rectangular metal foil which includes afirst uneven portion and a second uneven portion, into a cylindricalshape so as to overlap the first and second uneven portions with eachother, wherein the first uneven portion is composed of a projectingportion and a depressed portion formed on one edge of the metal foil,and the second uneven portion is composed of a depressed portion and aprojecting portion formed on another edge of the metal foil opposite tothe one edge. The projecting portion of the first uneven portion isdisposed so as to be pulled out near the bearing housing through thedepressed portion of the second uneven portion. The projecting portionof the second uneven portion is disposed so as to be pulled out near thebearing housing through the depressed portion of the first unevenportion. In addition, projecting portions of the first and second unevenportions pulled out near the bearing housing engage with the engagementgrooves.

In the radial foil bearing, the metal foil including the first andsecond uneven portions is wound into a cylindrical shape so as tooverlap the first and second uneven portions with each other, theprojecting portions of the uneven portions are pulled out near thebearing housing, and the projecting portions pulled out are engaged withthe engagement grooves formed on the inner circumferential surface ofthe bearing housing. Therefore, the top foil can be accommodated in andfixed to the bearing housing without performing spot welding or bendingmachining on the top foil and without occurrence of large reaction forcein the top foil from both ends toward the center thereof Thus, it ispossible to prevent the occurrence of distortion of the top foil, and tosufficiently decrease the distortion of the top foil.

In addition, the intermediate foil is provided between the top foil andthe back foil. Accordingly, even if shaft vibration (self-excitedvibration) occurs in the rotary shaft during rotation, the dampingeffect can be obtained using friction caused by slides between the topfoil and the intermediate foil and further between the intermediate foiland the back foil. Thus, using the damping effect, it is possible tosuppress the shaft vibration (self-excited vibration) and to easilysettle the shaft vibration. Furthermore, it is possible to increase therigidity of the top foil using the intermediate foil.

According to a second aspect of the present invention, in the firstaspect, intermediate foils are disposed overlapping with each other.

In this way. the damping effect can be further obtained using frictioncaused by a slide between the intermediate foils, and it is possible tofurther easily settle the shaft vibration (self-excited vibration).

According to a third aspect of the present invention, in the first orsecond aspect, the intermediate foil is formed of a rectangular metalfoil including an uneven portion which is composed of a projectingportion and a depressed portion formed on at least one edge of the metalfoil, and the projecting portion of the uneven portion engages with anengagement groove.

In this way, the intermediate foil can also be accommodated in and fixedto the bearing housing without performing spot welding or bendingmachining on the intermediate foil. Thus, the occurrence of distortionof the top foil due to the distortion formed in the intermediate foilcan be prevented.

According to a fourth aspect of the present invention, in any one of thefirst to third aspects, a through groove is formed on the innercircumferential surface of the bearing housing, wherein the throughgroove is continuous from one end to another end in the axial directionof the bearing housing. A fixing member is fitted into the throughgroove, wherein the fixing member divides the through groove in a lengthdirection thereof, thereby forming the engagement grooves. In addition,a restriction portion is provided in the through groove and the fixingmember, wherein the restriction portion restricts movement of the fixingmember in the length direction of the through groove.

In this way, since the through groove is formed continuous from one endto the other end in the axial direction of the bearing housing, it ispossible to easily form the through groove using, for example, wire-cutelectrical discharge machining.

In addition, even if a positional difference in the axial directionoccurs between the top foil and the bearing housing, the projectingportion of the top foil engaging with the engagement groove formed bydividing the through groove in the length direction is restricted by anend of the engagement groove, and the movement of the projecting portionis stopped, whereby the increase of the positional difference isprevented. Furthermore, since the restriction portion, which restrictsthe movement of the fixing member in the length direction of the throughgroove, is provided in the through groove and the fixing member, themovement of the fixing member is also stopped. Thus, the detachment ofthe top foil from the bearing housing is reliably prevented.

According to a fifth aspect of the present invention, in the fourthaspect, a locking recess is formed on an inner side surface of thethrough groove in the length direction of the through groove, whereinthe locking recess allows a tip portion of the projecting portion of thetop foil to be locked therein.

In this way, it is possible to easily perform the positioning and fixingof the projecting portion of the top foil by locking the projectingportion in the locking recess, and furthermore to improve the assemblyreproducibility of the top foil.

According to a sixth aspect of the present invention, in the fourth orfifth aspect, the restriction portion includes locking grooves and bentpieces, wherein the locking grooves are formed on both side surfaces ofthe bearing housing in a thickness direction of the bearing housing soas to communicate with both end portions of the through groove, and thebent pieces are formed at both end portions of the fixing member so asto be locked into the locking grooves.

In this way, the movement of the fixing member relative to the throughgroove in the length direction thereof can be reliably restricted, andthereby the detachment of the top foil from the bearing housing isreliably prevented. En addition, the locking grooves can be easilyformed using, for example, wire-cut electrical discharge machining.

According to a seventh aspect of the present invention, in any one ofthe first to sixth aspects, thin portions are formed on the one edge andon the other edge of the top foil, wherein the thin portions are thinnerthan an intermediate portion therebetween.

In this way, both end portions of the top foil are easily elasticallydeformed, and the occurrence of force (local preload) clamping therotary shaft is suppressed at both end portions of the top foil.

According to an eighth aspect of the present invention, in the seventhaspect, surfaces of the thin portions, which are opposite to surfacesthereof facing the rotary shaft, are formed so as to be depressed from asurface of the intermediate portion, which is opposite to a surfacethereof facing the rotary shaft.

In this way, a gap is formed between the surface of the thin portion,which is opposite to the surface thereof facing the rotary shaft, andthe back foil positioned on the outer circumferential surface-side ofthe thin portion. Therefore, the occurrence of force (local preload)clamping the rotary shaft is reliably prevented at the thin portions.

Effects of Invention

According to a radial foil bearing of the present invention, theoccurrence of distortion of the top foil can be prevented, and thedistortion of the top foil can be sufficiently decreased. Therefore, thedesigned favorable performance of the bearing can be obtained withrespect to the load capability and the dynamic characteristics (therigidity and the damping performance) thereof.

In addition, since the intermediate foil is provided therein, thedamping effect can be obtained using friction caused by a slide betweenthe intermediate foil and another foil, whereby it is possible to easilysettle the shaft vibration (self-excited vibration) of the rotary shaft,and furthermore to increase the rigidity of the top foil using theintermediate foil. Thus, it is possible to sufficiently improve thedynamic characteristics (the rigidity and the damping performance) ofthe bearing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an example of a turbo machine inwhich a radial foil bearing of the present invention is provided.

FIG. 2A is a side view of a radial foil bearing of a first embodiment ofthe present invention.

FIG. 2B is a cross-sectional view taken along A-A line of a bearinghousing in FIG. 2A.

FIG. 3A is a development view of a top foil.

FIG. 3B is a development side view of the top foil.

FIG. 3C is a development view of an intermediate foil.

FIG. 3D is a development side view of the intermediate foil.

FIG. 4A is a side view of a radial foil bearing of a modification of thefirst embodiment.

FIG. 4B is a development view of an intermediate foil.

FIG. 5A is a side view of a radial foil bearing of a modification of thefirst embodiment.

FIG. 5B is a development view of an intermediate foil.

FIG. 6A is a side view of a radial foil bearing of a second embodimentof the present invention.

FIG. 6B is a cross-sectional view taken along B-B line of a bearinghousing in FIG. 6A.

FIG. 6C is a development view of a top foil.

FIG. 6D is a development side view of the top foil.

FIG. 7A is a side view of a radial foil bearing of a third embodiment ofthe present invention.

FIG. 7B is a schematic view showing a main section of the innercircumferential surface of a bearing housing.

FIG. 8A is an exploded perspective view of a main section of the radialfoil bearing shown in FIG 7A.

FIG. 8B is a plan view showing a state where a fixing member is fittedinto a through groove.

FIG. 8C is a cross-sectional side view showing a state where the fixingmember is fitted into the through groove.

FIG. 9A is an exploded perspective view of a main section of the radialfoil bearing.

FIG. 9B is a cross-sectional view taken along C-C line in FIG 7A.

FIG. 10A is a side view in which a main section of FIG. 7A is flattenedand is schematically shown.

FIG. 10B is a view taken along D-D line in FIG. 10A.

FIG. 11 is an enlarged view of a main section of FIG. 7A.

FIG. 12A is a development view of a top foil of a fourth embodiment ofthe present invention.

FIG. 12B is a development side view of the top foil.

FIG. 12C is a development view of an intermediate foil.

FIG. 12D is a development side view of the intermediate foil.

FIG. 13A is a plan view showing a state where a fixing member is fittedinto a through groove.

FIG. 13B is a cross-sectional side view showing a state where the fixingmember is fitted into the through groove.

FIG. 14A is an exploded perspective view of a main section of a radialfoil bearing of a modification of a back foil structure.

FIG. 14B is a cross-sectional view of a main section of the radial foilbearing.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a radial foil bearing of the present invention is describedin detail with reference to the drawings. In the following drawings, thescale of each member is appropriately changed in order to show eachmember in a recognizable size.

FIG. 1 is a side view showing an example of a turbo machine in which aradial foil bearing of the present invention is provided. In FIG 1, areference numeral 1 represents a rotary shaft, a reference numeral 2represents an impeller provided in the tip portion of the rotary shaft,and a reference numeral 3 represents a radial foil bearing according tothe present invention. In addition, in FIG. 1, only one radial foilbearing is shown, and another radial foil bearing is omitted. However,in general, two radial foil bearings are provided in the axial directionof the rotary shaft 1, thereby configuring the support structure for therotary shaft 1. Accordingly, although not shown, two radial foilbearings 3 are also provided in this embodiment.

A thrust collar 4 is fixed to the rotary shaft 1 near the position atwhich the impeller 2 is formed, and thrust bearings 5 are disposed atboth sides of the thrust collar 4 so as to face the thrust collar 4.

The impeller 2 is disposed inside a housing 6 which is a stationaryportion, and a tip clearance 7 is formed between the impeller 2 and thehousing 6.

The radial foil bearing 3 is attached to the rotary shaft I at aposition nearer the center of the rotary shaft I than the thrust collar4 so as to encircle the rotary shaft I.

(First Embodiment)

FIGS. 2A and 2B are schematic views showing a first embodiment of aradial foil bearing provided in the turbo machine having the aboveconfiguration. As shown in FIG 2A, a radial foil bearing 3 of the firstembodiment is a cylindrical device which encircles the rotary shaft 1and which supports the rotary shaft 1. The radial foil bearing 3includes a cylindrical top foil 10 disposed facing the rotary shaft 1,an intermediate foil 11 disposed outside of the top foil 10 in theradial direction thereof, a back foil 12 disposed outside of theintermediate foil 11 in the radial direction, and a bearing housing 13disposed outside of the back foil 12 in the radial direction.

The bearing housing 13 is a cylindrical metal member which is theoutermost portion of the radial foil bearing 3 and accommodates the backfoil 12, the intermediate foil 11 and the top foil 10 at the insidethereof The bearing housing 13 is provided with engagement grooves 14which are formed on the inner circumferential surface of the bearinghousing 13 in the axial direction thereof. That is, as shown in FIG 2Bshowing the inner circumferential surface of the bearing housing 13, afirst engagement groove 14 a is formed on the inner circumferentialsurface of the bearing housing 13 on the entire length in the axialdirection of the bearing housing 13. In addition, second engagementgrooves 14 b are formed next to the first engagement groove 14 a (nextthereto in the circumferential direction) not on the entire length inthe axial direction of the bearing housing 13 but only on portions ofthe entire length.

In this embodiment, two second engagement grooves 14 b are formed on astraight line positioned next to the first engagement groove 14 a. Oneof the second engagement grooves 14 b is formed extending from one sideend (one end in the axial direction) toward the center of the bearinghousing 13, and the other thereof is formed extending from the otherside end toward the center of the bearing housing 13. Thus, the secondengagement grooves 14 b do not communicate with each other at a portionnear the center of the bearing housing 13, and bank portions 15 areformed at parts of the second engagement grooves 14 b near the abovecenter. wherein the bank portions 15 block the parts of the secondengagement grooves 14 b near the above center. In addition, the depths(depths in the radial direction) of the engagement grooves 14 a and 14 bare set to about 0.1 mm to several millimeters.

As shown in FIG. 2A, the back foil 12 is a member formed of a foil (thinsheet) and elastically supporting the intermediate foil 11 and the topfoil 10. As such a back foil 12, for example, it is possible to use abump foil, a sprig foil disclosed in Japanese Unexamined PatentApplication, First Publication No. 2006-57652 or Japanese UnexaminedPatent Application, First Publication No. 2004-270904, a back foildisclosed in Japanese Unexamined Patent Application, First PublicationNo. 2009-299748, or the like. In this embodiment, a bump foil is usedfor the back foil 12. However, the spring foil or the back foildescribed above may also be used for the back foil of the presentinvention.

As shown in FIG. 2A, in the back foil 12 (bump foil), a foil (thinsheet) is formed in a wave sheet shape and furthermore is formed in acylindrical shape along the inner circumferential surface of the bearinghousing 13. In this embodiment, the back foil 12 is arranged so that apredetermined space is formed between both ends of the back foil 12 inthe circumferential direction. That is, the back foil 12 is disposedcovering the inner circumferential surface of the bearing housing 13except the engagement grooves 14 (14 a and 14 b) and except the portionbetween the engagement grooves.

In the back foil 12 formed in a wave sheet shape, valley portionscontacting the bearing housing 13 and peak portions contacting theintermediate foil 11 are alternately formed in the circumferentialdirection of the radial foil bearing 3. In this way, the back foil 12,particularly, the peak portions contacting the intermediate foil 11,elastically supports the top foil 10 via the intermediate foil 11. Inaddition, fluid passageways are formed by the peak portions and by thevalley portions in the axial direction of the radial foil bearing 3.

In this embodiment, the back foil 12 (bump foil) is fixed to the bearinghousing 13 using spot welding or the like, similarly to the related art.

The top foil 10 is formed by being wound in a cylindrical shape alongthe inner surface of the back foil 12 (bump foil). The top foil 10 isprovided with a projecting portion 16 a formed on one edge (one end inthe circumferential direction) thereof and with projecting portions 16 bformed on the other edge thereof so that the projecting portions 16 aand 16 b engage with the engagement grooves 14 formed in the bearinghousing 13. As shown in FIG 3A being a development view of the top foil10, the top foil 10 is a member formed by winding a rectangular metalfoil, whose long side is in the circumferential direction of the bearingand whose short side is in the length direction of the bearing, in thearrow direction (the length direction of the long side: thecircumferential direction of the bearing) in FIG 3B being a side view ofthe metal foil, to be a cylindrical shape.

As shown in FIG 3A, the top foil 10 is provided with a first unevenportion 18 a (first top foil uneven portion) and with a second unevenportion 18 b (second top foil uneven portion), wherein the first unevenportion 18 a includes one projecting portion 16 a (top foil projectingportion) and two depressed portions 17 a (top foil depressed portions)which are formed on one edge (short side) of the top foil 10, and thesecond uneven portion 18 b includes two projecting portions 16 b (topfoil projecting portions) and one depressed portion 17 b (top foildepressed portion) which are formed on the other edge (short side) ofthe top foil 10 opposite to the one edge (short side). The depressedportion 17 b of the second uneven portion 18 b is formed correspondingto the projecting portion 16 a of the first uneven portion 18 a, and thedepressed portions 17 a of the first uneven portion 18 a are formedcorresponding to the projecting portions 16 b of the second unevenportion 18 b.

As shown in FIG. 2A, the intermediate foil 11 is disposed between theback foil 12 (bump foil) and the top foil 10, and is formed by beingwound in a cylindrical shape along the inner surface of the back foil 12(bump foil) similarly to the top foil 10. In this embodiment, theintermediate foil 11 is also provided with a projecting portion 19 aformed on one edge (one end in the circumferential direction) thereofand with projecting portions 19 b formed on the other edge thereof, andthe projecting portions 19 a and 19 b engage with the engagement grooves14 (14 a and 14 b).

As shown in FIG 3C being a development view of the intermediate foil 11,the intermediate foil 11 is a member formed by winding a rectangularmetal foil, whose long side is in the circumferential direction of thebearing and whose short side is in the length direction of the bearing,in the arrow direction (the length direction of the long side: thecircumferential direction of the bearing) in FIG 3D being a side view ofthe metal foil, to be a cylindrical shape. That is, the developed planarshape of the intermediate foil 11 is formed being the same as that ofthe top foil 10. In addition, as described below, the thickness of theintermediate foil 11 is formed sufficiently less than that of the topfoil 10.

As shown in FIG. 3C, the intermediate foil 11 is provided with a firstuneven portion 21 a (first intermediate foil uneven portion, unevenportion) and with a second uneven portion 21 b (second intermediate foiluneven portion, uneven portion), wherein the first uneven portion 21 aincludes one projecting portion 19 a (intermediate foil projectingportion) and two depressed portions 20 a (intermediate foil depressedportions) which are formed on one edge (short side) of the intermediatefoil 11, and the second uneven portion 21 b includes two projectingportions 19 b (intermediate foil projecting portions) and one depressedportion 20 b (intermediate foil depressed portion) which are formed onthe other edge (short side) of the intermediate foil 11 opposite to theone edge (short side). The depressed portion 20 b of the second unevenportion 21 b is formed corresponding to the projecting portion 19 a ofthe first uneven portion 21 a, and the depressed portions 20 a of thefirst uneven portion 21 a are formed corresponding to the projectingportions 19 b of the second uneven portion 21 b.

The intermediate foil 11 and the top foil 10 are overlapped with eachother, and furthermore as shown in FIG. 2A, they are wound in acylindrical shape so that the intermediate foil Ills positioned outsideof the top foil 10 in the radial direction (positioned near the backfoil 12) and the top foil 10 is positioned inside of the intermediatefoil 11 in the radial direction (positioned near the rotary shaft 1). Inaddition, the first uneven portion 18 a and the second uneven portion 18b of the top foil are overlapped with each other, and the first unevenportion 21 a and the second uneven portion 21 b of the intermediate foil11 are overlapped with each other. In this state, the projecting portion16 a of the top foil 10 and the projecting portion 19 a of theintermediate foil 11 together pass through the depressed portion 17 b ofthe second uneven portion 18 b of the top foil 10 and through thedepressed portion 20 b of the second uneven portion 21 b of theintermediate foil 11. Furthermore, the projecting portions 16 b of thetop foil 10 and the projecting portions 19 b of the intermediate foil 11together pass through the depressed portions 17 a of the first unevenportion 18 a of the top foil 10 and through the depressed portions 20 aof the first uneven portion 21 a of the intermediate foil 11.

The projecting portions 16 a and 19 a passed through the depressedportions 17 b and 20 b and the projecting portions 16 b and 19 b passedthrough the depressed portions 17 a and 20 a in the above way are pulledout near the bearing housing 13 as shown in FIG. 2A, and the tipportions of the projecting portions are engaged with the engagementgrooves 14 (14 a and 14 b) of the bearing housing 13. Therefore, the topfoil 10 and the intermediate foil 11 are disposed so that the movementthereof in the circumferential direction is restricted and so that theamount of the movement thereof becomes slight.

That is, the projecting portions 16 a, 16 b, 19 a and 19 b are disposedso that the tips thereof are not strongly thrust against the sidewallsurfaces or bottom surfaces of the engagement grooves 14 and so that thetips are positioned close thereto. Thus, at the time of the normaloperation of the rotary shaft 1, since the projecting. portions 16 a, 16b, 19 a and 19 b do not receive large reaction force from the engagementgrooves 14, the occurrence of distortions of the top foil 10 and of theintermediate foil 11 is prevented. In addition, even when unexpectedexternal force due to shaft deflection or the like of the rotary shaft 1is added to the radial foil bearing 3. the top foil 10 and theintermediate foil 11 are prevented from rotating inside the bearinghousing 13 and from being removed from a space between the bearinghousing 13 and the rotary shaft 1.

That is, when unexpected external force is added thereto, the projectingportions 16 a, 16 b, 19 a and 19 b are locked on the sidewall surfacesor bottom surfaces of the engagement grooves 14, whereby the detachmentof the projecting portions 16 a, 16 b, 19 a and 19 b from the engagementgrooves 14 is prevented. Thus, the top foil 10 is prevented fromrotating or being largely deformed. the projecting portions 16 a and 16b are prevented from sliding out of the depressed portions 17 b and 17a, and thus the top foil 10 is prevented from being detached from thebearing housing 13. In addition, the intermediate foil 11 is preventedfrom rotating or being largely deformed, the projecting portions 19 aand 19 b are prevented from sliding out of the depressed portions 20 band 20 a, and thus the intermediate foil 11 is prevented from beingdetached from the bearing housing 13.

As shown by dashed double-dotted lines in FIG 2B, particularly, theprojecting portions 16 b of the top foil 10 (and the projecting portions19 b of the intermediate foil 11) engaging with the second engagementgrooves 14 b are restricted from moving toward the center of the bearinghousing in the axial direction (inward of the bearing housing in theaxial direction) by the second engagement grooves 14 b. That is, thebank portions 15 are formed at parts of the second engagement grooves 14b near the center of the bearing housing 13. Accordingly, even if apositional difference in the axial direction occurs between the top foil10 and the bearing housing 13 or between the intermediate foil 11 andthe bearing housing 13, one of two projecting portions 16 b (theprojecting portions 19 b) contacts a bank portion 15 of an engagementgroove 14 b and is restricted thereby, whereby the movement thereof isstopped.

In addition, the projecting portion 16 a (the projecting portion 19 a)is inserted into the depressed portion 17 b (the depressed portion 20 b)formed between two projecting portions 16 b (the projecting portions 19b) in the axial direction. Accordingly, even if a positional differencein the axial direction occurs between the top foil 10 and the bearinghousing 13 or between the intermediate foil 11 and the bearing housing13, the projecting portion 16 a (the projecting portion 19 a) contactsone of two projecting portions 16 b (the projecting portions 19 b) andis restricted thereby, whereby the movement thereof is stopped.

In this way, the top foil 10 and the intermediate foil 11 are preventedfrom popping out of the bearing housing 13.

As shown in FIG. 3B, the top foil 10 in this embodiment is provided withthin portions 22 formed on a portion (one edge of the top foil 10) inwhich the first uneven portion 18 a is formed and on a portion (theother edge of the top foil 10) in which the second uneven portion 18 bis formed, wherein the thin portions 22 are thinner than theintermediate portion therebetween. As shown in FIG. 2A, the thinportions 22 are formed by being thinned into a state where outercircumferential surfaces of the top foil 10 (surfaces near theintermediate foil 11) are depressed from the outer circumferentialsurface of the above intermediate portion.

In order to form the thin portions 22. both end portions of the top foil10 are formed so as to have a desired thickness (thinness) using, forexample, etching, while the thickness thereof is controlled in 10 mmunit. Specifically, in a case where the diameter φ of the bearinghousing 13 is 35 mm and the length thereof in the axial direction is 35mm, if the thickness of the top foil 10 is about 100 μm, the thicknessof the thin portion 22 is set to about 80 μm.

In such etching, stress which occurs in the top foil 10 is very smallcompared to that of bending machining or the like, and thus theoccurrence of distortion of the top foil 10 is suppressed.

The length L in the circumferential direction of the thin portion 22shown in FIG. 3B is set to the length obtained by adding up the distancebetween two engagement grooves 14 next to each other in thecircumferential direction and the width of one peak in an end portion ofthe back foil 12 (bump foil), as shown in FIG 2A. The back foil 12 (bumpfoil) is formed so that the thickness thereof is about 100 μm, theheight of a peak thereof is about 500 μm, and the pitch of peaks (theinterval between peaks next to each other) is about 3 mm.

In this embodiment, the thin portions 22 are formed on both end portionsof the top foil 10. In addition, such thin portions may also be formedon the intermediate foil 11, or may be formed not on the top foil 10 butonly on the intermediate foil 11. However, in many cases, theintermediate foil 11 is formed to be very thin and has, for example, athickness of about 30 μm, and thus the intermediate foil 11 may not havea sufficient thickness in order to form the thin portions. Accordingly,the thin portions 22 are formed only on the top foil 10 in thisembodiment.

Since the thin portions 22 are formed on both end portions of the topfoil 10 in the above way, both end portions thereof (the thin portions22) are easily elastically deformed. Thus, both end portions thereof arecurved along a curved surface composing the inner circumferentialsurface of the bearing housing 13, and the intermediate foil 11 disposedoutside of the top foil 10 in the radial direction is also similarlycurved. Accordingly, the occurrence of force (local preload) clampingthe rotary shaft 1 at both end portions of the top foil 10 issuppressed, and similarly, the occurrence of the above force by theintermediate foil 11 is also suppressed.

Since the thin portions 22 are formed by being thinned so that the outercircumferential surfaces of both end portions of the top foil 10 aredepressed from the outer circumferential surface of the intermediateportion thereof a gap is formed between the thin portion 22 and one peakin an end portion of the back foil 12 which supports the outercircumferential surface of the thin portion 22 via the intermediate foil11. Accordingly, at the thin portions 22, the occurrence of force (localpreload) clamping the rotary shaft 1 is reliably prevented. In addition,the length L of the thin portion 22 in the circumferential direction maybe set to the length obtained by adding up the distance between twoengagement grooves 14 next to each other in the circumferentialdirection and the widths of about three peaks of an end portion of theback foil 12, instead of the example shown in FIG. 2A.

Next, the operation of the radial foil bearing 3 having the aboveconfiguration is described.

In a state where the rotary shaft 1 stops, the top foil 10 is pushed bythe back foil 12 via the intermediate foil 11 toward the rotary shaft 1,thereby closely contacting the rotary shaft 1. Additionally, in thisembodiment, since both end portions of the top foil 10 include the thinportions 22, the occurrence of force (local preload) clamping the rotaryshaft 1 at the thin portions 22 is suppressed.

When starting the rotary shaft 1 in the arrow P direction in FIG 2A, atfirst, the rotary shaft 1 starts rotating at a low speed, and thereafterthe rotation thereof is gradually accelerated and the rotary shaft 1rotates at a high speed. Then, as shown by the arrow Q in FIG. 2A, anambient fluid is led from a space between an end section of the top foil10 and of the intermediate foil 11 (the end section being near theprojecting portions 16 a and 19 a) and one end of the back foil 12, andflows into a space between the top foil 10 and the rotary shaft 1.Therefore, a fluid lubrication film is formed between the top foil 10and the rotary shaft 1.

At this time, in a transient state before the fluid lubrication film isformed, solid friction occurs between the rotary shaft 1 and the topfoil 10, and this friction makes resistance at the time of start-up.However, as described above, preload does not occur in both end portionsof the top foil 10. In addition, a side of the top foil 10 into which anambient fluid flows includes the thin portion 22 being flexible, and thetop foil 10 is configured to be easily separated from the rotary shaft1. Therefore, after the rotary shaft 1 is started, a fluid lubricationfilm is formed in a short time, and the rotary shaft 1 rotates in anon-contact state with respect to the top foil 10.

In the radial foil bearing 3 having the above configuration, theprojecting portions 16 a and 16 b pulled out from the depressed portions17 b and 17 a of the top foil 10 and the projecting portions 19 a and 19b pulled out from the depressed portions 20 b and 20 a of theintermediate foil 11 are engaged with the engagement grooves 14 (14 aand 14 b) formed on the inner circumferential surface of the bearinghousing 13. Therefore, the top foil 10 and the intermediate foil 11 canbe accommodated in and fixed to the bearing housing 13 withoutperforming spot welding or bending machining on the top foil 10 or onthe intermediate foil 11 and without occurrence of a large reactionforce therein from both ends toward the center thereof Accordingly,direct occurrence of distortion of the top foil 10 can be prevented, andoccurrence of distortion of the top foil 10 by reflecting, in the topfoil 10, the distortion occurring in the intermediate foil 11 can alsobe prevented. Thus, since the distortion of the top foil 10 issufficiently decreased, the designed favorable performance of thebearing can be obtained with respect to the load capability or thedynamic characteristics (the rigidity and the damping performance)thereof.

The intermediate foil 11 is disposed between the top foil 10 and theback foil 12, and thus, if shaft vibration (self-excited vibration)occurs in the rotary shaft 1 during rotation, film pressure variationdue to the vibration is transmitted from the top foil 10 to the backfoil 12 via the intermediate foil 11. At this time, slight flexure(changing due to a load) is caused to the top foil 10 due to loadvariation, and thereby, “slides” occur between the top foil 10 and theintermediate foil 11 and further between the intermediate foil 11 andthe back foil 12. The “slides” cause energy dissipation through frictionthereof, and thus the film pressure variation is damped. That is, thedamping effect can be obtained. Thus, using this damping effect, it ispossible to suppress the shaft vibration (self-excited vibration) and toeasily settle the shaft vibration. Furthermore, the intermediate foil 11can increase the rigidity of the top foil 10. Thus, the dynamiccharacteristics (the rigidity and the damping performance) of the radialfoil bearing 3 can be sufficiently improved.

In the manufacturing process with respect to the top foil 10 or to theintermediate foil 11, only the forming process of the uneven portions 18a and 18 b (the uneven portions 21 a and 21 b) through etching is addedthereto, and it is possible to remove spot welding in the related art orbending machining which may cause distortion. Thus, the difficulty ofthe manufacture thereof can be decreased, and the manufacturing costthereof can be reduced.

In addition, since the welding of the top foil 10 or of the intermediatefoil 11 on the bearing housing 13 is removed, assembly failures orassembly variations due to welding, defects are eliminated. Thus, thereproducibility thereof is improved, and excellent mass productivity isobtained.

In a structure in the related art in which one end of a top foil or ofan intermediate foil is spot-welded on a bearing housing so as to be afixed end and another end thereof is set to a free end, if a rotaryshaft is rotated in the reverse direction, the top foil or theintermediate foil may wind around the rotary shaft. hi contrast, theradial foil bearing 3 in this embodiment has approximately line symmetryas shown in FIG. 2A, and thus can accept the normal rotation and thereverse rotation of the rotary shaft 1 and can work equallytherebetween. Accordingly, the radial foil bearing can also be providedin a rotating machine in which the rotary shaft thereof rotates in thereverse direction.

Since the thin portions 22 are formed on both end portions of the topfoil 10, force (local preload) clamping the rotary shaft 1 also does notoccur at both end portions of the top foil 10 as described above. Thus,it is possible to prevent the starting torque from increasing due topreload, and to prevent the amount of heat generated during operationfrom exceeding the set value.

In addition, since the thin portions 22 are formed on both end portionsof the top foil 10, for example, a heat treatment process or the like,as in the related art, to fit both end portions of a top foil into aninner curved surface (inner circumferential surface) of a bearinghousing is unnecessary.

Furthermore, since the thin portions 22 are formed on both end portionsof the top foil 10, the end portion (corresponding to the free end inthe related art) of the top foil 10, into which an ambient fluid flows,has flexibility, and thus the ambient fluid easily flows into a spacebetween the top foil 10 and the rotary shaft 1 as described above.

Accordingly, a fluid lubrication film is formed at a low rotation speed,and thus the startability is improved.

In the above-described first embodiment, the development shape of theintermediate foil 11 is formed being the same as the development shapeof the top foil 10 as shown in FIGS. 3A to 3D, and the projectingportions 19 a and 19 b of the intermediate foil 11 together with theprojecting portions 16 a and 16 b of the top foil 10 are engaged withthe engagement grooves 14 corresponding thereto. However, as shown in,for example, FIGS. 4A and 4B, the intermediate foil 11 may be providedwith a pair of projecting portions 19 b formed only on one edge (shortside) thereof, and the projecting portions 19 b may be engaged with apair of second engagement grooves 14 b. In this case, even if apositional difference in the axial direction occurs between theintermediate foil 11 and the bearing housing 13, one of two projectingportions 19 b contacts a bank portion 15 of a second engagement groove14 b shown in FIG 2B and is restricted thereby, whereby the movementthereof is stopped. Therefore, the intermediate foil 11 is preventedfrom popping out of the bearing housing 13.

As shown in FIGS. 5A and 5B, the uneven portions 21 a and 21 b may notbe formed on both edges (short sides) of the intermediate foil 11, andthe intermediate foil 11 may be formed having a rectangular shape bycutting off both short sides thereof. In this case, as shown in FIG. 5A,the intermediate foil 11 is disposed without engaging with an engagementgroove 14. However, since the intermediate foil 11 is inserted betweenthe back foil 12 and the top foil 10 and is held therebetween throughfriction, the intermediate foil 11 is prevented from popping out of thebearing housing 13 even if a positional difference in the axialdirection occurs between the intermediate foil 11 and the bearinghousing 13.

(Second Embodiment)

Next, a second embodiment of a radial foil bearing of the presentinvention is described. FIGS. 6A to 6D are schematic views showing thesecond embodiment of a radial foil bearing provided in the turbo machineshown in FIG. 1, and in FIG. 6A, a reference numeral 30 represents aradial foil bearing. The radial foil bearing 30 is different from theradial foil bearing 3 shown in FIG. 2A, in the shapes of a top foil andof an intermediate foil, and in the shapes of engagement grooves of abearing housing corresponding thereto.

As shown in FIG. 6C. a top foil 31 of the radial foil bearing 30 in thisembodiment is provided with a first uneven portion 34 a and a seconduneven portion 34 b, wherein the first uneven portion 34 a includes aprojecting portion 32 a and a depressed portion 33 a which are formed onone edge (short side) thereof, and the second uneven portion 34 bincludes a projecting portion 32 b and a depressed portion 33 b whichare formed on the other edge (short side) thereof opposite to the oneedge (short side). The depressed portion 33 b of the second unevenportion 34 b is formed corresponding to the projecting portion 32 a ofthe first uneven portion 34 a, and the depressed portion 33 a of thefirst uneven portion 34 a is formed corresponding to the projectingportion 32 b of the second uneven portion 34 b.

The depressed portion 33 b of the second uneven portion 34 b is formedso that the projecting portion 32 a passes through the depressed portion33 b when the top foil 31 is wound in a cylindrical shape so as tooverlap the first and second uneven portions 34 a and 34 b with eachother. Furthermore, the depressed portion 33 a of the first unevenportion 34 a is formed so that the projecting portion 32 b passesthrough the depressed portion 33 a when the top foil 31 is wound in acylindrical shape. Additionally, in this embodiment, the widths (widthsin the axial direction) of the depressed portions 33 b and 33 a areformed sufficiently greater than the widths of the projecting portions32 a and 32 b corresponding thereto.

As shown in FIG. 6A, an intermediate foil 35 is disposed between a backfoil 12 (bump foil) and the top foil 31. The intermediate foil 35 iswound in a cylindrical shape along the inner surface of the back foil 12(bump foil), similarly to the top foil 31. In this embodiment, theintermediate foil 35 is formed having the same development shape as thatof the top foil 31 shown in FIG. 6C. Thus, although not shown, theintermediate foil 35 is formed including projecting portions anddepressed portions which have the same shapes as those of the projectingportions 32 a and 32 b and the depressed portions 33 a and 33 b.

The intermediate foil 35 is also formed so that the projecting portionof one edge thereof passes through the depressed portion of the otheredge thereof when being wound in a cylindrical shape, similarly to thetop foil 31. That is, the intermediate foil 35 and the top foil 31 areoverlapped with each other similarly to the first embodiment,furthermore they are wound in a cylindrical shape so that theintermediate foil 35 is positioned outside of the top foil 31 in theradial direction and the top foil 10 is positioned inside of theintermediate foil 11 in the radial direction, and thereafter theprojecting portions thereof are engaged with engagement groovescorresponding thereto.

Engagement grooves 37 are formed on the inner circumferential surface ofa bearing housing 36, at positions corresponding to the projectingportions 32 a and 32 b and the like. That is, as shown in FIG. 6Bshowing the inner circumferential surface of the bearing housing 36, twoengagement grooves 37 are formed on the inner circumferential surface ofthe bearing housing 36 not on the entire length in the axial directionof the bearing housing 36 but only on portions of the entire length.

One of the engagement grooves 37 is formed extending from one side end(one end in the axial direction) toward the center of the bearinghousing 36, and the other thereof is formed extending from the otherside end toward the center of the bearing housing 36.

The radial foil bearing 30 having the above configuration can alsoobtain operation and effect equivalent to that of the radial foilbearing 3 shown in FIG 2A. That is, the projecting portions 32 a and 32b and the like pulled out from the depressed portions 33 b and 33 a andthe like are engaged with the engagement grooves 37 formed on the innercircumferential surface of the bearing housing 36. Therefore, the topfoil 31 and the intermediate foil 35 can be accommodated in and fixed tothe bearing housing 36 without performing spot welding or bendingmachining on the top foil 31 or on the intermediate foil 35 and withoutoccurrence of large reaction force from both ends toward the centerthereof. Thus, direct occurrence of distortion of the top foil 31 can beprevented, and occurrence of distortion of the top foil 31 byreflecting, in the top foil 31, the distortion occurring in theintermediate foil 35 can also be prevented. Consequently, since thedistortion of the top foil 31 is sufficiently decreased, the designedfavorable performance of the bearing can be obtained with respect to theload capability or the dynamic characteristics (the rigidity and thedamping performance) thereof.

The intermediate foil 35 is disposed between the top foil 31 and theback foil 12, and thus, if shaft vibration (self-excited vibration)occurs in the rotary shaft 1 during rotation, it is possible to suppressthe shaft vibration (self-excited vibration) and to easily settle theshaft vibration, using the above-described damping effect. Furthermore,the intermediate foil 35 can increase the rigidity of the top foil 31.Thus, the dynamic characteristics (the rigidity and the dampingperformance) of the radial foil bearing 30 can be sufficiently improved.

As shown in FIG. 6D, thin portions 22 are formed on both end portions ofthe top foil 31, and thus force (local preload) clamping the rotaryshaft 1 also does not occur at both end portions of the top foil 31 asdescribed above. Thus, it is possible to prevent the starting torquefrom increasing due to preload, and to prevent the amount of heatgenerated during operation from exceeding the set value.

As shown by dashed double-dotted lines in FIG. 6B, the projectingportions 32 a and 32 b engaging with the engagement grooves 37 arerestricted from moving toward the center of the bearing housing in theaxial direction (inward of the bearing housing in the axial direction)by bank portions 15 of the engagement grooves 37, and thus the top foil31 can be prevented from popping out of the bearing housing 36.Similarly, the intermediate foil 35 can also be prevented from poppingout of the bearing housing 36.

In the above-described second embodiment, the development shape of theintermediate foil 35 is formed being the same as the development shapeof the top foil 31, and the projecting portions (not shown) of theintermediate foil 35 together with the projecting portions 32 a and 32 bof the top foil 31 are engaged with the engagement grooves 37corresponding thereto. However, similarly to the case shown in FIG. 4Bin the first embodiment, the intermediate foil 35 may be provided with aprojecting portion (not shown) formed only on one edge (short side)thereof Furthermore, similarly to the case shown in FIG. 5B, theintermediate foil 35 may be formed having a rectangular shape by cuttingoff both short sides thereof In this case, the intermediate foil 35 isinserted between the back foil 12 and the top foil 31 and is heldtherebetween using friction, and thus the intermediate foil 35 isprevented from popping out of the bearing housing 36 even if apositional difference in the axial direction occurs between theintermediate foil 35 and the bearing housing 36.

(Third Embodiment)

Next, a third embodiment of a radial foil bearing of the presentinvention is described. FIGS. 7A and 7B are schematic views showing thethird embodiment of a radial foil bearing provided in the turbo machineshown in FIG. 1, and in FIG. 7A, a reference numeral 40 represents aradial foil bearing. The radial foil bearing 40 is different from theradial foil bearing 3 shown in FIG. 2A, in the structure of anengagement groove of a bearing housing, and in the structure of a backfoil.

A bearing housing 41 is a cylindrical metal member which is theoutermost portion of the radial foil bearing 40, and accommodates a backfoil 42, an intermediate foil 11 and a top foil 10 at the inside thereofThe intermediate foil 11 and the top foil 10 are formed havingapproximately the same structures as those of the intermediate foil 11and of the top foil 10 in the first embodiment shown in FIGS. 3A to 3D.

A through groove 43 is formed on the inner circumferential surface ofthe bearing housing 41 in the axial direction of the bearing housing 41.As shown in FIG. 7B showing a main section of the inner circumferentialsurface of the bearing housing 41, the through groove 43 is formed onthe inner circumferential surface of the bearing housing 41 on theentire length of the bearing housing 41 so as to be continuous from oneend to the other end in the axial direction thereof. The through groove43 is formed so that the length thereof is the same as the length(length in the axial direction) of the bearing housing 41, the openingwidth (width of the opening in the circumferential direction) thereof isabout 3 to 4 mm, and the depth (depth in the radial direction) thereofis about 1.5 to 2.5 mm.

Locking grooves 44 are formed at both end portions (both end portions inthe axial direction) of the through groove 43 so as to communicate withthe through groove 43. As shown in FIG. 8A being an exploded perspectiveview of a main section of the radial foil bearing 40, the lockinggrooves 44 are grooves formed by cutting out parts from both sidesurfaces (both end surfaces in the axial direction) of the bearinghousing 41. The locking grooves 44 are formed in the thickness direction(the radial direction) from the inner circumferential edge (the innercircumferential surface) to the outer circumferential edge (the outercircumferential surface) of the bearing housing 41.

Additionally, in this embodiment, the width (width in thecircumferential direction) of the locking groove 44 is formedsufficiently greater than that of the through groove 43 in order toreliably communicate the locking groove 44 with the through groove 43.

Locking recesses 45 are formed on both inner side surfaces (surfacesfacing each other in the circumferential direction) of the throughgroove 43. The locking recesses 45 are groove-shaped recesses formed inthe length direction on the entire length of the through groove 43, andin this embodiment, are formed in a cross-sectional U-shape (asemicircular shape) whose maximum depth (depth in the circumferentialdirection) is about 0.2 to 0.3 mm. In addition, the locking recesses 45are formed at a depth position being 1 mm or less from the opening ofthe through groove 43, that is, from the inner circumferential surfaceof the bearing housing 41. Accordingly, as described below, the tips ofprojecting portions of the top foil 10 and of the intermediate foil 11can be locked in the locking recesses 45.

Wire-cut electrical discharge machining is suitably used in order toform the through groove 43 and the locking recesses 45. That is, whenforming a groove continuous from one end to the other end in the axialdirection of the bearing housing 41, such as the through groove 43 orthe groove-shaped locking recess 45, using the wire-cut electricaldischarge machining, a wire thereof is moved along the edge of thecross-sectional shape of the groove, and thereby each groove can beeasily and accurately formed. Particularly, in this embodiment, if thewire-cut electrical discharge machining is adopted, the through groove43 and the locking recesses 45 positioned on both inner side surfaces ofthe through groove 43 can be easily formed through a series ofmachining, and therefore it is possible to sufficiently decrease themachining cost of the through groove 43 and the locking recesses 45.

In the locking groove 44, a groove is formed continuous from the outercircumferential surface to the inner circumferential surface of thebearing housing 41. Accordingly, if wire-cut electrical dischargemachining is adopted, it is possible to sufficiently decrease themachining cost thereof. However, since the machining of the lockinggroove 44 does not require particular high accuracy, it is possible todo the cutting work with, for example, an end mill, or the like.

A fixing member 46 is fitted and locked in the through groove 43 and inthe locking grooves 44. As shown in FIG. 8A, in FIG. 8B being a planview of the through groove 43 and the fixing member 46, and in FIG. 8Cbeing a cross-sectional side view of the through groove 43 and thefixing member 46, the fixing member 46 includes a bar-shaped (squarepole-shaped) base portion 47 which is fitted and accommodated in thethrough groove 43, a pair of bent pieces 48 which are formed on bothends of the base portion 47 and which are locked in the pair of lockinggrooves 44, and two partition pieces 49 which are formed in anintermediate portion of the base portion 47 and which project oppositeto the bent pieces 48.

The base portion 47 is formed so that the height thereof is about 0.5 to1.5 mm and so that the top surface thereof (the surface in which thepartition piece 49 is provided) is depressed about 1 mm from the openingof the through groove 43. The bent piece 48 is formed having a lengthwhich is approximately equivalent to the distance between the bottomsurface of the through groove 43 and the outer circumferential surfaceof the bearing housing 41. Accordingly, the bent piece 48 contacts thelocking groove 44 with a sufficient contact area and is prevented fromprojecting from the outer circumferential surface of the bearing housing41.

A restriction portion of the present invention is composed of the bentpieces 48 and the locking grooves 44 provided communicating with thethrough groove 43. That is, the pair of bent pieces 48 are locked in thelocking grooves 44 provided at both ends of the through groove 43, andthus the bearing housing 41 is held between the pair of bent pieces 48in the axial direction. Therefore, movement of the fixing member 46 isrestricted in the length direction of the through groove 43 (in theaxial direction of the bearing housing 41), and the movement thereof issubstantially prevented except for a movement based on a clearance.

As shown in FIGS. 8B and 8C, the partition pieces 49 are formed at twopositions which divide the base portion 47 into approximately threeportions, that is, which divide the through groove 43 into approximatelythree grooves. The partition piece 49 is formed so that the level of thetop thereof is the same as that of the opening of the through groove 43or so that the top slightly projects from the opening of the throughgroove 43. For example, the partition piece 49 may project approximatelyhalf of the height of the back foil 42 from the opening of the throughgroove 43. The partition pieces 49 divide the through groove 43 intoapproximately three grooves in the length direction thereof, andthereby, three engagement grooves 50 are formed inside the throughgroove 43 by the fixing member 46.

That is, the fixing member 46 is fitted and locked in the lockinggrooves 44 and in the through groove 43 from the side of the innercircumferential surface of the bearing housing 41, and thereby the threeengagement grooves 50 can be easily formed. The depth of each engagementgroove 50 is set to about 1 mm, and the locking recesses 45 open at bothinner side surfaces of each engagement groove 50.

The fixing member 46 can be manufactured by, for example, machining ametal plate of stainless steel or the like having a thickness (thicknessin the circumferential direction) of about 3 to 4 mm using wire-cutelectrical discharge machining.

As shown in FIG. 7A, engagement projections 63 a are formed in thebearing housing 41 using locking members 60 in order to lock the backfoil 42 (described below). That is, as shown in FIG 9A being an explodedperspective view of a main section of the radial foil bearing 40,engagement recesses 61 are formed on both side surfaces of the bearinghousing 41 so as to be opposite to each other, wherein each engagementrecess 61 is formed in a groove shape extending from the innercircumferential edge (inner circumferential surface) toward the outercircumferential edge (outer circumferential surface) of the bearinghousing 41. A pair of engagement recesses 61 are formed at positionsopposite to each other in the axial direction of the bearing housing 41.As shown in FIG 7A, the engagement recesses 61 in this embodiment areformed at positions which divide each side surface of the bearinghousing 41 into approximately three areas in the circumferentialdirection thereof The locking members 60 are locked in the engagementrecesses 61. In addition, in this embodiment, the through groove 43 isarranged in an intermediate position between two engagement recesses 61in the engagement recesses 61 disposed at three positions in one sidesurface of the bearing housing 41.

As shown in FIG. 9A, grooves 62 are formed on the inner circumferentialsurface of the bearing housing 41, wherein the groove 62 is positionedbetween the engagement recesses 61 opposite to each other andcommunicates with each of the engagement recesses 61. The depth of thegroove 62 is set to be less than that of the engagement recess 61, thatis, than the depth toward the outer circumferential surface of thebearing housing 41 (in this embodiment, equivalent to the thickness ofthe bearing housing 41). Therefore, in this embodiment, a step is formedbetween the engagement recess 61 and the groove 62.

The locking member 60 is locked in the engagement recesses 61 and in thegroove 62.

The locking member 60 includes a pair of engagement arms 63 engagingwith the engagement recesses 61, and a connection portion 64 connectingthe engagement arms 63, and thus is formed in an H-shape. As shown inFIG 9B being a cross-sectional view taken along C-C line in FIG 7A, theconnection portion 64 is engaged with and accommodated in the groove 62,and is formed so as not to project outside of the groove 62 (inside ofthe bearing housing 41 in the radial direction). Specifically, the depthof the groove 62 is set to about 1 to 2 mm, and thus the height of theconnection portion 64 is also set to about 1 to 2 mm.

Each of the pair of engagement arms 63 is formed extending upward andextending downward (in the radial direction) with respect to theconnection portion 64, and thereby the locking member 60 is formed in anH-shape as described above. A portion of the engagement arm 63 extendingupward, that is, a portion of the engagement arm 63 opposite to anotherportion thereof engaging with the engagement recess 61, projects fromthe inner circumferential surface of the bearing housing 41, and therebycomposes the engagement projection 63 a which engages with an engagementnotch 42 d of a back foil piece 42 a (described below).

A portion of the engagement arm 63 extending downward (outward of thebearing in the radial direction) is locked on the above-described stepbetween the engagement recess 61 and the groove 62. Therefore, movementof the locking member 60 is restricted in the axial direction withrespect to the bearing housing 41.

The engagement arm 63 or the connection portion 64 of the locking member60 may be formed in a square pole shape as shown in FIG. 9A, or in acolumnar shape (a round bar shape). The thickness of the engagement arm63 or of the connection portion 64 is set to about 0.3 to 0.5 mm. Thelocking member 60 can be manufactured by, for example, processing ametal foil of stainless steel or the like having a thickness less than0.5 mm into an H-shape using etching or wire-cut electrical dischargemachining.

The groove 62 can be formed through wire-cut electrical dischargemachining, similarly to the through groove 43. In addition, theengagement recesses 61 can be formed through wire-cut electricaldischarge machining, cutting work using an end mill, or the like,similarly to the locking grooves 44. That is, the through groove 43 andthe grooves 62 can be continuously formed through wire-cut electricaldischarge machining, and the locking grooves 44 and the engagementrecesses 61 can be continuously formed through wire-cut electricaldischarge machining or the like. Thus, it is possible to decrease themachining cost of the bearing housing 41.

After the grooves 62 and the engagement recesses 61 are formed in thisway, the locking member 60 is fitted and locked in the engagementrecesses 61 and in the groove 62 from the side of the innercircumferential surface of the bearing housing 41, and thereby theengagement projections 63 a can be easily formed.

As shown in FIG. 7A, the back foil 42 is a member formed of a foil (thinsheet) and elastically supporting the intermediate foil 11 and the topfoil 10, similarly to the back foil 12 in the first embodiment. In thisembodiment, a bump foil is also used for the back foil 42.

In this embodiment, the back foil 42 (bump foil) includes three (aplurality of) back foil pieces 42 a which are disposed in thecircumferential direction of the intermediate foil 11. Each back foilpiece 42 a is a member in which a foil (thin sheet) is formed in a wavesheet shape and in which the side shape thereof is set to be anapproximately arc shape as a whole, and all three the back foil pieces42 a are formed having the same shape and dimensions. Thus, the backfoil pieces 42 a are disposed so as to divide the inner circumferentialsurface of the bearing housing 41 into approximately three areas.

At positions between which the through groove 43 is disposed, the backfoil pieces 42 a are disposed forming a comparatively large gaptherebetween, and at other positions, the back foil pieces 42 a aredisposed so that end portions thereof are adjacent to each other.According to this configuration, the three back foil pieces 42 a areformed in an approximately cylindrical shape as a whole, and aredisposed along the inner circumferential surface of the bearing housing41.

As shown in FIG 10A in which a main section of FIG. 7A is flattened andis schematically shown, in the back foil piece 42 a formed in a wavesheet shape in the above way, flattened valley portions 42 b contactingthe bearing housing 41 and curved peak portions 42 c contacting theintermediate foil 11 are alternately formed in the circumferentialdirection of the bearing housing 41. Accordingly, the back foil pieces42 a elastically support the top foil 10 via the intermediate foil 11.particularly through the peak portions 42 c contacting the intermediatefoil 11. In addition, fluid passageways are formed by the peak portions42 c and the valley portions 42 b, wherein the fluid passageway extendsin the axial direction of the radial foil bearing 40.

As shown in FIG. 10B being a view taken along D-D line in FIG. 10A,engagement notches 42 d are formed on both side edges (both ends in theaxial direction) of a circumferentially center portion (a center portionin the circumferential direction of the bearing housing 41) of each backfoil piece 42 a. As shown in FIG. 10A, the engagement notches 42 d areformed in a valley portion 42 b of the back foil piece 42 a, and theengagement notch 42 d is a notch formed by cutting out, from theflattened valley portion 42 b positioned between the peak portions 42 c,a rectangular part extending from the edge toward the center of thevalley portion 42 b.

The engagement notch 42 d is formed at a position corresponding to theengagement projection 63 a of the locking member 60 provided in thebearing housing 41, that is, at a position overlapping with theengagement projection 63 a. So as to engage with the engagementprojection 63 a, the engagement notch 42 d is formed having a length andwidth which are approximately the same as the length and width of theengagement projection 63 a. Specifically, the width of the engagementnotch 42 d in the circumferential direction of the bearing housing 41 isset to about 0.2 to 0.4 mm, and the length of the engagement notch 42 din the axial direction is set to about 1 to 2 mm.

In order to prevent occurrence of burr or distortion due to machining ona back foil piece, it is preferable that the engagement notch 42 d beformed by performing etching or electrical discharge machining on afoil. That is, it is preferable that the engagement notches 42 d beformed in a foil using etching or electrical discharge machining, andthereafter, press molding be performed on the foil in order to form thepeak portions 42 c and the valley portions 42 b, thereby forming theback foil piece 42 a.

Based on this configuration, as shown in FIGS. 9A and 10A, theengagement notch 42 d of the back foil piece 42 a engages with theengagement projection 63 a of the bearing housing 41.

In this way, the engagement notch 42 d of the back foil piece 42 aengages with the engagement projection 63 a extending upward of theengagement arm 63, and in this state, the three back foil pieces 42 aare disposed on the inner circumferential surface of the bearing housing41. Therefore, the locking member 60, particularly, the connectionportion 64 thereof, is covered with the back foil piece 42 a, wherebythe detachment of the locking member 60 from the bearing housing 41 isprevented.

As shown in FIG 7A, the intermediate foil 11 and the top foil 10 haveapproximately the same structures as those of the intermediate foil 11and of the top foil 10 in the first embodiment shown in FIGS. 3A to 3D,respectively. The intermediate foil 11 and the top foil 10 areoverlapped with each other, and then are wound in a cylindrical shapealong the inner surface of the back foil 42 composed of three back foilpieces 42 a. The top foil 10 is provided with a projecting portion 16 aformed on one edge thereof and with projecting portions 16 b formed onanother edge thereof and the projecting portions 16 a and 16 b engagewith the engagement grooves 50 in the through groove 43 formed in thebearing housing 41. In addition, the intermediate foil 11 is providedwith a projecting portion 19 a formed on one edge thereof and withprojecting portions 19 b formed on another edge thereof, and theprojecting portions 19 a and 19 b together with the projecting portions16 a and 16 b engage with the engagement grooves 50 in the throughgroove 43.

The top foil 10 is provided with a first uneven portion 18 a and asecond uneven portion 18 b (refer to FIG. 3A) which are formed so that agap is formed between the projecting portion 16 a and each of the pairof projecting portions 16 b when the projecting portion 16 a of thefirst uneven portion 18 a passes through the depressed portion 17 b ofthe second uneven portion 18 b wherein the gap corresponds to the widthof the partition piece 49 of the fixing member 46. Similarly, theintermediate foil 11 is provided with a first uneven portion 21 a and asecond uneven portion 21 b (refer to FIG. 3C) which are formed so that agap is formed between the projecting portion 19 a and each of the pairof projecting portions 19 b when the projecting portion 19 a of thefirst uneven portion 21 a passes through the depressed portion 20 b ofthe second uneven portion 21 b, wherein the gap corresponds to the widthof the partition piece 49 of the fixing member 46.

In addition, the projecting portions 16 a, 16 b, 19 a and 19 b areformed so that the widths thereof correspond to the lengths of theengagement grooves 50 formed by the through groove 43 and by the fixingmember 46 and the widths are approximately the same as the lengths.

As shown in FIG. 7A, the projecting portions 16 a and 16 b passedthrough the depressed portions 17 b and 17 a and the projecting portions19 a and 19 b passed through the depressed portions 20 b and 20 a arepulled out near the bearing housing 41, and the tips thereof are engagedwith the engagement grooves 50 of the bearing housing 41. In thisembodiment, as shown in FIG 11 being an enlarged view of a main sectionof FIG. 7A. the tips of the projecting portions 16 a. 16 b, 19 a and 19b are inserted into and engaged with the engagement grooves 50 in thethrough groove 43, and thereafter are further inserted into the lockingrecesses 45, to be locked therein. Therefore, the top foil 10 and theintermediate foil 11 are arranged so that the movement thereof in thecircumferential direction is restricted and the amount of the movementis maintained to be slight.

That is, the projecting portions 16 a. 16 b, 19 a and 19 b are arrangedso that the tips thereof are not strongly thrust against inner surfacesof the locking recesses 45 and so that the edge surfaces of the tipsthereof contact inner surfaces of the locking recesses 45. Accordingly,at the time of the normal operation of the rotary shaft 1, since theprojecting portions 16 a, 16 b, 19 a and 19 b do not receive largereaction force from the locking recesses 45 or from the engagementgrooves 50, the occurrence of distortion of the top foil 10 or of theintermediate foil 11 is prevented. In addition, even when unexpectedexternal force due to shaft deflection or the like of the rotary shaft 1is added to the radial foil bearing 40, both of the top foil 10 and theintermediate foil 11 are prevented from rotating inside the bearinghousing 41 and from being removed from a space between the bearinghousing 41 and the rotary shaft 1.

That is, when unexpected external force is added thereto, the projectingportions 16 a, 16 b, 19 a and 19 b are strongly locked on inner surfacesof the locking recesses 45, and thereby the projecting portions 16 a. 16b, 19 a and 19 b are prevented from getting out of the locking recesses45 and further of the engagement grooves 50. Accordingly, the top foil10 is prevented from rotating or being largely deformed, the projectingportions 16 a and 16 b are prevented from sliding out of the depressedportions 17 b and 17 a, and thus the top foil 10 is prevented from beingdetached from the bearing housing 41. In addition, the intermediate foil11 is prevented from rotating or being largely deformed, the projectingportions 19 a and 19 b are prevented from sliding out of the depressedportions 20 b and 20 a, and thus the intermediate foil 11 is preventedfrom being detached from the bearing housing 41.

The movement of the projecting portions Ia, 16 b, 19 a and 19 b in theaxial direction is restricted by the partition pieces 49 of the fixingmember 46 which form the engagement grooves 50. That is, both sides ofthe projecting portion 16 a are restricted by the partition pieces 49,whereby the first uneven portion 18 a including the projecting portion16 a is restricted from moving in the axial direction. In addition, bothsides of the projecting portion 19 a are restricted by the partitionpieces 49, whereby the first uneven portion 21 a including theprojecting portion 19 a is restricted from moving in the axialdirection.

The two projecting portions 16 b are restricted by the two partitionpieces 49 from moving in opposite directions in the axial direction,whereby the second uneven portion 18 b including the projecting portions16 b is restricted from moving in the axial direction. In addition, thetwo projecting portions 19 b are restricted by the two partition pieces49 from moving in opposite directions in the axial direction, wherebythe second uneven portion 21 b including the projecting portions 19 b isrestricted from moving in the axial direction. In this way, since themovement of the top foil 10 and the intermediate foil 11 is restrictedin the axial direction of the bearing housing 41, the top foil 10 andthe intermediate foil 11 are prevented from popping out of the bearinghousing 41.

Next, the operation of the radial foil bearing 40 having the aboveconfiguration is described.

In a state where the rotary shaft 1 stops, the top foil 10 is pushed bythe back foil 42 (three back foil pieces 42 a) via the intermediate foil11 toward the rotary shaft 1, thereby closely contacting the rotaryshaft 1. In addition, in this embodiment, since both end portions of thetop foil 10 include the thin portions 22 similarly to the firstembodiment, the occurrence of force (local preload) clamping the rotaryshaft 1 in the thin portions 22 is suppressed.

When starting the rotary shaft 1 in the arrow P direction in FIG. 7A, atfirst, the rotary shaft 1 starts rotating at a low speed, and thereafterthe rotation thereof is gradually accelerated and the rotary shaft 1rotates at a high speed. Then, as shown by the arrow Q in FIG 7A, anambient fluid is led from a space between one end section of the topfoil 10 and of the intermediate foil 11 and one end of the back foilpiece 42 a, and flows into a space between the top foil 10 and therotary shaft 1. Therefore, a fluid lubrication film is formed betweenthe top foil 10 and the rotary shaft 1.

The film pressure of the fluid lubrication film is added to the top foil10, and presses, via the top foil 10 and the intermediate foil 11, eachpeak portion 42 c of the back foil pieces 42 a contacting theintermediate foil 11. Then, the back foil pieces 42 a are pressed by thetop foil 10, and thus the peak portions 42 c are pressed and extended,whereby the back foil pieces 42 a start moving on the bearing housing 41in the circumferential direction thereof That is, since the back foilpieces 42 a (the back foil 42) elastically support the top foil 10 viathe intermediate foil 11, the back foil pieces 42 a are deformed in thecircumferential direction at the time of receiving a load from the topfoil 10, and thereby accept the flexure of the top foil 10 and supportit.

However, as shown in FIGS. 9A and 9B, the engagement projections 63 a ofthe locking member 60 engage with the engagement notches 42 d providedin side edges of the back foil piece 42 a, whereby the back foil piece42 a is prevented from rotating in the circumferential direction on theinner circumferential surface of the bearing housing 41. Thus, althougheach peak portion 42 c of the back foil piece 42 a is deformed (moves)in the circumferential direction in a state where the engagement notch42 d engaging with the engagement projection 63 a is the fixed point(fixed end) thereof, the center of the back foil piece 42 a is preventedfrom deviating from the original position thereof.

When the back foil piece 42 a is deformed (moves) in the circumferentialdirection, the back foil piece 42 a receives the influence of frictionwith the bearing housing 41 or with the intermediate foil 11. Therefore,although both end portions of the back foil piece 42 a, that is, freeends, are easily deformed (easily move), it is difficult to deformportions thereof near the above fixed point (fixed end). Accordingly, adifference in support rigidity may occur between a portion near the freeend and a portion near the fixed end of the back foil piece 42 a.

However, in this embodiment, the engagement notch 42 d is formed in thecenter of the back foil piece 42 a in the circumferential direction, andthus the fixed point by the engagement projection 63 a is arranged inthe center of the back foil piece 42 a in the circumferential direction.Therefore, the distance between the fixed end and the free end isdecreased, and the above difference in support rigidity is decreased.Furthermore, in this embodiment, since the back foil 42 is divided intothree back foil pieces 42 a, the distance between the fixed end and thefree end is further decreased compared to a case where the back foil 42is composed of one foil, and thus the difference in support rigiditybetween a portion near the free end and a portion near the fixed endthereof is further decreased.

At the time the rotary shaft 1 rotates at a high speed, the engagementprojections 63 a hold the movement of the back foil piece 42 a in theaxial direction. Therefore, even if unexpected impact or the like isadded thereto, the detachment of the back foil piece 42 a from thebearing housing 41 can be prevented.

Additionally, in a transient state before the fluid lubrication film isformed, solid friction occurs between the rotary shaft 1 and the topfoil 10, and this friction makes resistance at the time of start-up.However, as described above, preload does not occur in both end portionsof the top foil 10. In addition, a side of the top foil 10 into which anambient fluid flows includes the thin portion 22 being flexible, and thetop foil 10 is configured to be easily separated from the rotary shaft1. Therefore, after the rotary shaft 1 is started, a fluid lubricationfilm is formed in a short time, and the rotary shaft 1 rotates in anon-contact state with respect to the top foil 10.

In the radial foil bearing 40 having the above configuration, theprojecting portions I 6 a and 16 b pulled out from the depressedportions 17 b and 17 a of the top foil and the projecting portions 19 aand 19 b pulled out from the depressed portions 20 b and 20 a of theintermediate foil 11 are engaged with the engagement grooves 50 whichare formed in the through groove 43 on the inner circumferential surfaceof the bearing housing 41 using the fixing member 46. Therefore, the topfoil 10 and the intermediate foil 11 can be accommodated in and fixed tothe bearing housing 41 without performing spot welding or bendingmachining on the top foil 10 or on the intermediate foil 11 and withoutthe occurrence of a large reaction force therein from both ends towardthe center thereof. Accordingly, direct occurrence of distortion of thetop foil 10 can be prevented, and occurrence of distortion of the topfoil 10 by reflecting, in the top foil 10, the distortion occurring inthe intermediate foil 11 can also be prevented. Thus, since thedistortion of the top foil 10 is sufficiently decreased, the designedfavorable performance of the bearing can be obtained with respect to theload capability or the dynamic characteristics (the rigidity and thedamping performance) thereof.

The intermediate foil 11 is disposed between the top foil 10 and theback foil 42, and thus, if shaft vibration (self-excited vibration)occurs in the rotary shaft 1 during rotation, the damping effect can beobtained using friction caused by slides between the top foil 10 and theintermediate foil 11 and further between the intermediate foil 11 andthe back foil 42. Therefore, it is possible to suppress the shaftvibration (self-excited vibration) and to easily settle the shaftvibration, using the damping effect. Furthermore, the intermediate foil11 can increase the rigidity of the top foil 10. Thus, the dynamiccharacteristics (the rigidity and the damping performance) of the radialfoil bearing 40 can be sufficiently improved.

Since the through groove 43 is formed continuous from one end to theother end in the axial direction of the bearing housing 41, the throughgroove 43 can be easily formed through wire-cut electrical dischargemachining, and thus the machining cost thereof can be decreased so as tobe low.

In addition, even if a positional difference in the axial directionoccurs between the top foil 10 and the bearing housing 41 or between theintermediate foil 11 and the bearing housing 41, the projecting portions16 a, 16 b, 19 a and 19 b, which engage with the engagement grooves 50formed by dividing the through groove 43 in the length directionthereof, are restricted by the ends (the partition pieces 49) of theengagement grooves 50 and the movement thereof is stopped, and thereforethe increase of the positional difference can be prevented. Furthermore,since the restriction portion, which restricts the fixing member 46 frommoving in the length direction of the through groove 43, is formed ofthe locking grooves 44 of the through groove 43 and of the bent pieces48 of the fixing member 46, the movement of the fixing member 46 canalso be stopped. Thus, the detachment of the top foil 10 and of theintermediate foil 11 from the bearing housing 41 can be reliablyprevented.

Since the tips of the projecting portions 16 a and 16 b of the top foil10 and of the projecting portions 19 a and 19 b of the intermediate foil11 are engaged with the locking recesses 45 formed on inner sidesurfaces of the through groove 43, it is possible to easily perform thepositioning and locking of the projecting portions 16 a, 16 b, 19 a and19 b, and furthermore to improve the assembly reproducibility of the topfoil 10 or the intermediate foil 11.

In addition, since the welding of the top foil 10 or of the intermediatefoil 11 on the bearing housing 41 is removed, assembly failures orassembly variations due to welding defects are eliminated. Thus, thereproducibility thereof is improved, and excellent mass productivity isobtained.

Since the thin portions 22 are formed on both end portions of the topfoil 10, force (local preload) clamping the rotary shaft 1 also does notoccur at both end portions of the top foil 10 as described above. Thus,it is possible to prevent the starting torque from increasing due topreload, and to prevent the amount of heat generated during operationfrom exceeding the set value.

In addition, since the thin portions 22 are formed on both end portionsof the top foil 10, for example, a heat treatment process, as in therelated art, to fit both end portions of a top foil into an inner curvedsurface (inner circumferential surface) of a bearing housing isunnecessary.

Furthermore, since the thin portions 22 are formed on both end portionsof the top foil 10, the vicinity of an end (corresponding to the freeend in the related art) of the top foil 10, into which an ambient fluidflows, has flexibility, and thus the ambient fluid easily flows into aspace between the top foil 10 and the rotary shaft 1 as described above.

Accordingly, a fluid lubrication film is formed at a low rotation speed.and thus the startability is improved.

The engagement notch 42 d formed at each of both side edges of the backfoil piece 42 a is engaged with the engagement projection 63 a formed ateach of both side ends of the inner circumferential surface of thebearing housing 41, whereby the back foil piece 42 a is fixed to thebearing housing 41. Accordingly, the back foil piece 42 a can beaccommodated in and fixed to the bearing housing 41 without performingspot welding or bending machining on the back foil piece 42 a. Thus, theoccurrence of distortion of the top foil 10 due to spot welding on theback foil 42 (the back foil pieces 42 a) or due to the distortion of theback foil 42 can be prevented, and the distortion of the top foil 10 canbe sufficiently decreased. Consequently, the designed favorableperformance of the bearing can be obtained with respect to the loadcapability or the dynamic characteristics (the rigidity and the dampingperformance) thereof.

In the above-described third embodiment, the development shape of theintermediate foil 11 is formed being the same as the development shapeof the top foil 10, similarly to the first embodiment, and theprojecting portions 19 a and 19 b of the intermediate foil 11 togetherwith the projecting portions 16 a and 16 b of the top foil 10 areengaged with the engagement grooves 50 corresponding thereto. However,similarly to the first embodiment, as shown in, for example, FIGS. 4Aand 4B, the intermediate foil 11 may be provided with only a pair ofprojecting portions 19 b formed on one edge (short side) thereof, andthe projecting portions 19 b may be engaged with the engagement grooves50 corresponding thereto. In this case, even if a positional differencein the axial direction occurs between the intermediate foil 11 and thebearing housing 41, one of two projecting portions 19 b contacts apartition piece 49 and is restricted thereby. whereby the movementthereof is stopped. Therefore, the intermediate foil 11 is preventedfrom popping out of the bearing housing 41.

As shown in FIGS. 5A and 5B, the uneven portions 21 a and 21 b may notbe formed on both edges (short sides) of the intermediate foil 11, andthe intermediate foil 11 may be formed having a rectangular shape bycutting off both short sides thereof In this case, although theintermediate foil 11 is disposed without engaging with the engagementgrooves 50, the intermediate foil 11 is inserted between the back foil42 and the top foil 10 and is held therebetween using friction. Thus,the intermediate foil 11 is prevented from popping out of the bearinghousing 41 even if a positional difference in the axial direction occursbetween the intermediate foil 11 and the bearing housing 41.

(Fourth Embodiment)

Next, a fourth embodiment of a radial foil bearing of the presentinvention is described.

The radial foil bearing in this embodiment can also be used for a radialfoil bearing provided in the turbo machine shown in FIG. 1. This radialfoil bearing is different from the radial foil bearing 40 in the thirdembodiment, in the shapes of a top foil and of an intermediate foil, andin the shapes of engagement grooves of a bearing housing correspondingthereto.

As shown in FIGS. 12A and 12B, a top foil 70 of the radial foil bearingin this embodiment is formed having the same shape as that of the topfoil 31 shown in FIGS. 6C and 6D. As shown in FIGS. 12C and 12D, anintermediate foil 80 is formed having the same shape as that of the topfoil 70.

As shown in FIGS. 12A and 12B, the top foil 70 is provided with a firstuneven portion 73 a and a second uneven portion 73 b, wherein the firstuneven portion 73 a includes a projecting portion 71 a and a depressedportion 72 a which are formed on one edge (short side) of the top foil70, and the second uneven portion 73 b includes a projecting portion 71b and a depressed portion 72 b which are formed on another edge (shortside) thereof opposite to the one edge (short side). The depressedportion 72 b of the second uneven portion 73 b is formed correspondingto the projecting portion 71 a of the first uneven portion 73 a, and thedepressed portion 72 a of the first uneven portion 73 a is formedcorresponding, to the projecting portion 71 b of the second unevenportion 73 b. In addition, as shown in FIG. 12B. the top foil 70 is alsoprovided with thin portions 22 formed on both end portions thereof.

The depressed portion 72 b of the second uneven portion 73 b is formedso that the projecting portion 71 a passes through the depressed portion72 b when the top foil 70 is wound in a cylindrical shape so as tooverlap the first uneven portion 73 a and the second uneven portion 73 bwith each other. Similarly, the depressed portion 72 a of the firstuneven portion 73 a is formed so that the projecting portion 71 b passesthrough the depressed portion 72 a when the top foil 70 is wound in acylindrical shape. In this embodiment. the widths (widths in the axialdirection) of the depressed portions 72 b and 72 a are formedsufficiently greater than the widths of the projecting portions 71 a and71 b, respectively. In addition, the projecting portions 71 a and 71 bare formed so that the widths thereof correspond to the lengths ofengagement grooves (described below) and the widths are approximatelythe same as the lengths, similarly to the third embodiment.

As shown in FIGS. 12C and 12D, the intermediate foil 80 is provided witha first uneven portion 83 a (uneven portion) and a second uneven portion83 b (uneven portion), wherein the first uneven portion 83 a includes aprojecting portion 81 a and a depressed portion 82 a which are formed onone edge (short side) of the intermediate foil 80, and the second unevenportion 83 b includes a projecting portion 81 b and a depressed portion82 b which are formed on another edge (short side) thereof opposite tothe one edge (short side). The depressed portion 82 b of the seconduneven portion 83 b is formed corresponding to the projecting portion 81a of the first uneven portion 83 a, and the depressed portion 82 a ofthe first uneven portion 83 a is formed corresponding to the projectingportion 81 b of the second uneven portion 83 b.

The depressed portion 82 b of the second uneven portion 83 b is formedso that the projecting portion 81 a passes through the depressed portion82 b when the intermediate foil 80 is wound in a cylindrical shape so asto overlap the first uneven portion 83 a and the second uneven portion83 b with each other. Similarly, the depressed portion 82 a of the firstuneven portion 83 a is formed so that the projecting portion 81 b passesthrough the depressed portion 82 a when the intermediate foil 80 iswound in a cylindrical shape. In this embodiment, the widths (widths inthe axial direction) of the depressed portions 82 b and 82 a are formedsufficiently greater than the widths of the projecting portions 81 a and81 b, respectively In addition, the projecting portions 81 a and 81 bare formed so that the widths thereof correspond to the lengths ofengagement grooves (described below) and the widths are approximatelythe same as the lengths, similarly to the third embodiment.

As shown in FIGS. 13A and 13B, a fixing member 90 is fitted and lockedin a through groove 43 formed on the inner circumferential surface of abearing housing 41. The fixing member 90 includes a bar-shaped (squarepole-shaped) base portion 47 which is fitted and accommodated in thethrough groove 43, a pair of bent pieces 48 which are formed on bothends of the base portion 47 and which are locked in locking grooves 44,and a partition portion 91 which is formed in an intermediate portion ofthe base portion 47 and which projects opposite to the bent pieces 48.

The fixing member 90 is different from the fixing member 46 shown inFIGS. 8B and 8C, only in that one partition portion 91 is formed insteadof two partition pieces 49. Accordingly, in this embodiment, as shown inFIGS. 13A and 13B, engagement grooves 92 are formed on both sides of thepartition portion 91, that is, on two positions in total. In addition,the partition portion 91 is formed sufficiently longer than thepartition piece 49, and as shown in FIG. 13B, no engagement groove isformed at the position corresponding to the partition portion 91. Thatis, in this embodiment, the engagement grooves 92 are not formed on theentire length of the through groove 43. The engagement groove 92 areformed at the positions in which the projecting portions 71 a and 71 bof the top foil 70 shown in FIG. 12A and the projecting portions 81 aand 81 b of the intermediate foil 80 shown in FIG. 12C are disposed.

According to the radial foil bearing having the above configuration, itis possible to obtain operation and effect equivalent to that of theradial foil bearing 40 in the third embodiment. That is, the projectingportions 71 a and 71 b pulled out from the depressed portions 72 b and72 a and the projecting portions 81 a and 81 b pulled out from thedepressed portions 82 b and 82 a are engaged with the engagement grooves92 which are formed in the through groove 43 on the innercircumferential surface of the bearing housing 41 using the fixingmember 90. Therefore, the top foil 70 and the intermediate foil 80 canbe accommodated in and fixed to the bearing housing 41 withoutperforming spot welding or bending machining on the top foil 70 or onthe intermediate foil 80 and without occurrence of a large reactionforce therein from both ends toward the center thereof Accordingly,direct occurrence of distortion of the top foil 70 can be prevented, andoccurrence of distortion of the top foil 70 by reflecting, in the topfoil 70, the distortion occurring in the intermediate foil 80 can alsobe prevented. Thus, since the distortion of the top foil 70 issufficiently decreased, the designed favorable performance of thebearing can be obtained with respect to the load capability or thedynamic characteristics (the rigidity and the damping performance)thereof.

The intermediate foil 80 is disposed between the top foil 70 and a backfoil 42, and thus, if shaft vibration (self-excited vibration) occurs inthe rotary shaft 1 during rotation, it is possible to suppress the shaftvibration (self-excited vibration) and to easily settle the shaftvibration, using the above-described damping effect. Furthermore, theintermediate foil 80 can increase the rigidity of the top foil 70. Thus,the dynamic characteristics (the rigidity and the damping performance)of the radial foil bearing can be sufficiently improved.

Since the thin portions 22 are formed on both end portions of the topfoil 70, force (local preload) clamping the rotary shaft 1 also does notoccur at both end portions of the top foil 70 as described above. Thus,it is possible to prevent the starting torque from increasing due topreload, and to prevent the amount of heat generated during operationfrom exceeding the set value.

In the above-described fourth embodiment, the development shape of theintermediate foil 80 is formed being the same as the development shapeof the top foil 70, and the projecting portions 81 a and 81 b of theintermediate foil 80 together with the projecting portions 71 a and 71 bof the top foil 70 are engaged with the engagement grooves 92corresponding thereto. However, similarly to the case in the thirdembodiment, the intermediate foil 80 may be provided with only aprojecting portion formed on one edge (short side) thereof Furthermore,the intermediate foil 80 may be formed having a rectangular shape bycutting off both short sides thereof. In this case, the intermediatefoil 80 is inserted between the back foil 42 and the top foil 70 and isheld therebetween using friction, and thus the intermediate foil 80 isprevented from popping out of the bearing housing 41 even if apositional difference in the axial direction occurs between theintermediate foil 80 and the bearing housing 41.

The present invention is not limited to the above first to fourthembodiments and is limited only by the scopes of the attached claims.The shape, the combination or the like of each component shown in theabove-described embodiments is an example, and additions, omissions,replacements, and other modifications of configurations based on designrequests or the like can be adopted within the scope of and notdeparting from the gist of the present invention.

For example, in the above embodiments, an intermediate foil composed ofone sheet is used. However, a plurality of intermediate foils may bedisposed overlapping with each other, to be multi-layered. In this way,if the multi-layered intermediate foils are disposed between a back foiland a top foil, the damping effect obtained using friction caused by aslide between the intermediate foils is added to the damping effectobtained using friction caused by a slide between the top foil and theintermediate foil or between the intermediate foil and the back foil.Thus, it is possible to further suppress the shaft vibration(self-excited vibration) of a rotary shaft and to further easily settlethe shaft vibration.

In order to improve the damping effect of a radial foil bearing, asdescribed above, the adoption of multi-layered intermediate foils iseffective. However, in the related art, since an intermediate foil isspot-welded on a bearing housing, it is necessary to control thethickness of the intermediate foil so as to prevent melt of theintermediate foil through the welding, and thus the thickness of theintermediate foil is set to be approximately equivalent to that of a topfoil. Therefore, if intermediate foils having such a thickness aredisposed overlapping with each other, to be multi-layered, the rigidityof the bearing surface (the rigidity obtained by adding up these of thetop foil and of the intermediate foils) becomes very high, and thus thebearing surface may not properly accept film pressure variation of afluid lubrication film caused by shaft vibration. As a result, thedamping effect based on a “slide” between foils may not be easilyobtained.

In contrast, in the above embodiments, without welding an intermediatefoil on a bearing housing, by engaging a projecting portion thereof withan engagement groove, the intermediate foil is fixed between a back foiland a top foil, and accordingly, the intermediate foil can be formedhaving a sufficiently less thickness than that of the top foil. Thus,while the rigidity of the bearing surface is suppressed to be anappropriate level (strength), a multi-layered structure of intermediatefoils can be adopted.

In the top foil or the intermediate foil, each of the first and seconduneven portions is formed including one or two projecting portions andone or two depressed portions. However, the number of the projectingportions or of the depressed portions may be three or more.

In addition, the thin portion 22 may be formed by, for example, etchingboth surfaces thereof, to be thinned.

In the first and second embodiments. the back foil 12 composed of onesheet is used and is fixed to the bearing housing through spot weldingor the like. However, the back foil 42 composed of three back foilpieces 42 a shown in the third and fourth embodiments may be usedtherein instead of such a back foil 12, and may be fixed to the bearinghousing through the locking members 60.

On the other hand, in the third and fourth embodiments, the back foil 12composed of one sheet shown in the first and second embodiments may beused therein instead of the back foil 42 composed of three back foilpieces 42 a, and may be fixed to the bearing housing.

In the third and fourth embodiments, the engagement projection, which isengaged with the engagement notch 42 d of the back foil piece 42 a, maynot be formed using the locking member 60. The engagement projection maybe formed directly on the inner circumferential surface of the bearinghousing 41.

In addition, in the third and fourth embodiments, as shown in FIGS. 9Aand 9B, the engagement notch 42 d of the back foil piece 42 a is engagedwith the engagement projection 63 a formed using the locking member 60,and thereby the back foil piece 42 a is fixed to the bearing housing 41.However, a back foil of the present invention is not limited to such astructure. For example, each back foil piece 42 a may be fixed to thebearing housing 41 using a locking member 51 as shown in FIGS. 14A and14B.

As shown in FIGS. 14A and 14B, the locking member 51 includes a pair ofengagement legs 52 and a connection portion 53 which is disposed at oneend of each engagement leg 52 and which connects the engagement legs 52.One engagement leg 52 engages with the engagement recess 61 positionedon one side surface of the bearing housing 41 and with the engagementnotch 42 d of the back foil piece 42 a, and the other engagement leg 52engages with the engagement recess 61 positioned on the other sidesurface of the bearing housing 41 and with the engagement notch 42 d ofthe back foil piece 42 a. As shown in FIG. 14B, the length of theengagement leg 52 is set to be approximately equivalent to the lengthobtained by adding up the thickness of the bearing housing 41 and thethickness of the back foil piece 42 a. In addition, as shown in FIGS.14A and 14B, the connection portion 53 is disposed between the valleyportion 42 b of the back foil piece 42 a and the top foil 10.

According to the above configuration, the locking member 51 functions asa fixing member which fixes the back foil piece 42 a to the bearinghousing 41 because the engagement legs 52 engage with the engagementrecesses 61 of the bearing housing 41 and with the engagement notches 42d of the back foil piece 42 a. In addition, since the connection portion53 is covered with the top foil 10, the locking member 51 is preventedfrom being detached from the back foil piece 42 a. Therefore, it ispossible to reliably fix the back foil piece 42 a to the bearing housing41.

In the third and fourth embodiments, the back foil 42 is composed ofthree back foil pieces 42 a. However, the back foil 42 may be a singlemember in which one metal foil is formed in a substantially cylindricalshape. Furthermore, in a case where a plurality of back foil pieces 42 aare used. the back foil 42 may be composed of two, four or more backfoil pieces 42 a.

In addition, in the above embodiments, the bearing housing is formed ina cylindrical shape. However, an annular flange may be integrally formedon one side surface or on each of both side surfaces of a bearinghousing, and the whole shape of the bearing housing may be formed in anapproximately cylindrical shape. The bearing housing can be easilyattached to the housing or the like of a turbo machine, by forming theflange.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a radial foil bearing whichsupports a rotary shaft so as to encircle the rotary shaft.

DESCRIPTION OF REFERENCE SIGNS

-   1 rotary shaft-   3, 30, 40 radial foil bearing-   10, 31, 70 top foil-   11, 35, 80 intermediate foil-   12, 42 back foil (bump foil)-   13, 36, 41 bearing housing-   14, 37, 50, 92 engagement groove-   16 a, 16 b, 32 a, 32 b, 71 a, 71 b projecting portion-   17 a, 17 b, 33 a, 33 b, 72 a, 72 b depressed portion-   18 a, 34 a, 73 a first uneven portion-   18 b, 34 b 73 b second uneven portion-   19 a, 19 b, 81 a, 81 b projecting portion-   20 a, 20 b, 82 a, 82 b depressed portion-   21 a, 83 a first uneven portion (uneven portion)-   21 b, 83 b second uneven portion (uneven portion)-   42 a back foil piece-   43 through groove-   44 locking groove-   45 locking recess-   46, 90 fixing member-   47 base portion-   48 bent piece-   49 partition piece-   91 partition portion

The invention claimed is:
 1. A radial foil bearing used for supporting arotary shaft so as to encircle the rotary shaft, the radial foil bearingcomprising: a cylindrical top foil disposed so as to face the rotaryshaft; an intermediate foil disposed outside of the top foil in a radialdirection thereof; a back foil disposed outside of the intermediate foilin the radial direction; and a cylindrical bearing housing accommodatingthe top foil, the intermediate foil and the back foil, whereinengagement grooves are formed on an inner circumferential surface of thebearing housing in an axial direction thereof, the top foil is formed bywinding a rectangular metal foil which includes a first uneven portionand a second uneven portion, into a cylindrical shape so as to overlapthe first and second uneven portions with each other, the first unevenportion being composed of a projecting portion and a depressed portionformed on one edge of the metal foil, the second uneven portion beingcomposed of a depressed portion and a projecting portion formed onanother edge of the metal foil opposite to the one edge, the projectingportion of the first uneven portion is disposed so as to be pulled outnear the bearing housing through the depressed portion of the seconduneven portion, the projecting portion of the second uneven portion isdisposed so as to be pulled out near the bearing housing through thedepressed portion of the first uneven portion, and the projectingportions of the first and second uneven portions pulled out near thebearing housing engage with the engagement grooves.
 2. The radial foilbearing according to claim 1, wherein the intermediate foil has amulti-layered structure including foils overlapping with each other. 3.The radial foil bearing according to claim 1, wherein the intermediatefoil is formed of a rectangular metal foil including an uneven portionwhich is composed of a projecting portion and a depressed portion formedon at least one edge of the metal foil, and the projecting portion ofthe uneven portion engages with one of the engagement grooves.
 4. Theradial foil bearing according to claim 1, wherein a through groove isformed on the inner circumferential surface of the bearing housing, thethrough groove being continuous from one end to another end in the axialdirection of the bearing housing, a fixing member is fitted into thethrough groove, the fixing member dividing the through groove in alength direction thereof, thereby forming the engagement grooves, and arestriction portion is provided in the through groove and the fixingmember, the restriction portion restricting movement of the fixingmember in the length direction of the through groove.
 5. The radial foilbearing according to claim 4, wherein a locking recess is formed on aninner side surface of the through groove in the length direction of thethrough groove, the locking recess allowing a tip portion of theprojecting portion of the top foil to be locked therein.
 6. The radialfoil bearing according to claim 4, wherein the restriction portionincludes locking grooves and bent pieces, the locking grooves beingformed on both side surfaces of the bearing housing in a thicknessdirection of the bearing housing so as to communicate with both endportions of the through groove, the bent pieces being formed at both endportions of the fixing member so as to be locked into the lockinggrooves.
 7. The radial foil bearing according to claim 4, wherein thinportions are formed on the one edge and on the other edge of the topfoil, the thin portions being thinner than an intermediate portiontherebetween.
 8. The radial foil bearing according to claim 7, whereinsurfaces of the thin portions, which are opposite to surfaces thereoffacing the rotary shaft, are formed so as to be depressed from a surfaceof the intermediate portion, which is opposite to a surface thereoffacing the rotary shaft.
 9. The radial foil bearing according to claim1, wherein thin portions are formed on the one edge and on the otheredge of the top foil, the thin portions being thinner than anintermediate portion therebetween.
 10. The radial foil bearing accordingto claim 9, wherein surfaces of the thin portions, which are opposite tosurfaces thereof facing the rotary shaft, are formed so as to bedepressed from a surface of the intermediate portion, which is oppositeto a surface thereof facing the rotary shaft.